Oligopeptidases, and the emergence of the prolyl oligopeptidase family.

Oligopeptidases are endopeptidases that are not proteinases in the strict sense, since they do not hydrolyse peptide bonds in proteins, but act only on smaller polypeptides or oligopeptides. These enzymes apparently perform important, specialized biological functions that include the modification or destruction of peptide messenger molecules. Oligopeptidases have few naturally occurring inhibitors, and their distinctive specificity prevents them from interacting with alpha 2-macroglobulin, unlike the great majority of endopeptidases. The specificity of these specialized endopeptidases doubtless depends upon the three-dimensional structure of the active site, but no crystallographic structure is yet available for an oligopeptidase. Study of the primary structure of prolyl oligopeptidase has recently shown that it is a member of a new family of serine-type peptidases most of which are exopeptidases. The alignment of the sequences leads to the identification of some catalytic triad residues that have not yet been elucidated experimentally.